The insect pictured (at the link below) above began life as a caterpillar
walking upon numerous legs. It was later transformed into an entirely
different insect with the wings of a butterfly. This transformation
is called metamorphosis.
How does evolution explain the metamorphosis from a caterpillar
to a butterfly?

The advocates of evolution explain this insect and its metamorphosis
generally as follows:
"... [the development of] a nymph stage aided their survival
[as a caterpillar] and it was added to their life cycle. Eventually
at some point a nymph formed a cocoon around itself before maturing
to the adult stage. This enabled it to survive a winter and emerge
full grown. So, by a long step by step process, the Complete Metamorphosis
cycle did arise. This is not absolutely proven." Donning, Daryl
P. "Metamorphosis and Evolution." NCSE Reports 14(2) 11.
Quoted by Association for Rational Thought.

This explanation and others like it are pure conjecture.

How can random beneficial mutations and survival of the fittest
create a creature that, at a predetermined time in its life, is
transformed into an entirely different creature? How did environmental
pressures create the mechanism for transforming a caterpillar into
a butterfly? How? Where is the evidence? Where is a credible, thorough
explanation? There is none.
The theory of evolving metamorphosis cannot be tested nor can it
be observed nor can it be accounted for or adequately explained
in evolutionary terms.

Not does evolution fail to provide any adequate explanation for
the metamorphosis of a caterpillar into a butterfly, but it also
cannot come near to explaining how either the caterpillar or the
butterfly ever came into existence. In this regard, let us consider
the photograph above.

Consider that the insect pictured above has a brain. Evolution teaches
that the brain of this insect evolved through thousands of years
of accidental mutations that somehow benefitted the improved insect
and enabled it to survive to the prejudice of other insects who
did not enjoy the same beneficial mutations.

Evolutionists have written very little about how the brain in insects
evolved. The concept of insects' brains has been relegated to words
like "primitive" and "simple:"

Evolution's explanation is brief: the brains of insects like the
butterfly and the honeybee are "simple" brains.

The brain of the honeybee is "relatively simple." Evolution
Research - General Evolution News, August 5, 2006
The truth is that the brains of these insects are complex beyond
comprehension. Other than pure conjecture and generalities, the
theory of random beneficial mutations and survival of the fittest
makes no attempt whatever to explain how the brain of the butterfly
and the brain of the moth could have possibly evolved.

The brains of "simple" insects such as butterflies, bees
and flies are probably smaller that the head of a pin yet they compute
at the rate of a billion computations in 1/1000 of a second, or
a trillion logically organized computations per second. For instance,
the brain of the common housefly computes at approximately 1011
computations per second when merely resting:
"Using the criterion of joules per operation, the brain [of
the honeybee] is about 7 or 8 orders of magnitude more power efficient
than the best of the silicon chips. A direct consequence of their
efficiency is that brains can perform many more operations per second
than even the newest supercomputers. The fastest digital computers
are capable of around 109 computations per second; the brain of
the common housefly, for example, performs about 1011 operations
per second when merely resting."

Sejnowski,
T.J. and Churchland, P.S. The Computational Brain (MIT Press, 1992),
p. 9 (emphasis in the original). Sejnowski and Churchland are well
recognized in the field of neurobiology and computational neuroscience
and are professors at the University of California. See also Sejnowski,
T.J. and Churchland, P.S., 1992, Byte Magazine, October, 1992, p.
137 relating to the computing power of the brain of the honeybee.
Author's note: a simple internet search provides information relating
to Terrence J. Sejnowski and P.S. Churchland.

The evolutionary explanation of how these brains came to be is simple.
Accidental incremental changes moved the insect up and up, and with
each new computational cycle somehow the insect was better able
to survive, until at the end there was a fully integrated living
supercomputer the size of a pinhead that would compute at a trillion
interrelated and logical cycles each second. And all of these minute
electrical computations were supposedly designed by random beneficial
mutations that were directed by the survival of the fittest. It
is fortunate indeed that these simple brains instantaneously make
calculations of speed and distance, wing beat and direction, process
in nanoseconds millions upon millions of bits of electrical digital
code to create an instantaneous three dimentional representation
of external reality (vision), process equally complicated digital
codes for smell, for touch, for location, direction and orientation
and for memory, and process observations and make instantaneous
threat recognition and threat avoidance, and recognize and locate
food and reproduce.

It is not rational thought to conclude that unobserved beneficial
mutations and survival of the fittest caused caterpillars turn into
butterflies and endowed them with brains the size of pinheads that
are more powerful than supercomputers.

Scales on the Wings

Somewhere inside the butterfly and moth, there are written instructions
that set forth the exact placement of thousands upon thousands of
tiny scales on their wings. These scales are individually colored
with the obvious intention of forming colored designs. These scales
are clearly not random, but were specifically intended to create
a pattern and are organized into discrete rows and matching colors.

Here is a close up of the yellow spot that is just under the "li"
in the photograph of the insect at the top of this page:
Note how each tiny scale is the same size but colored differently
and placed so as to create a design. There is even a discrete fading
from brown to yellow. All of the scales are in rows and each one
is in its place.

There is an obvious intent to create an overall design of color
on the wing.

Where are the accidental scales falling randomly over the surface
of the wing? Where are the yellow scales falling into the brown?
Evolution's explanation for this is (and has to be) that all of
the butterflies with some misplaced scales died because the butterflies
with the advantage of properly placed scales were better able to
survive. Is this rational thought?

Did the accidental arrangement of thousands (millions?) of scales
into this pattern really contribute to the survival of some primordial
butterfly? Why are there no butterflies without (lovely) patterns
on their wings? Why are they beautiful?
Note also how the scales, like pixels on the computer screen, vary
in intensity of color so as to create a picture intended to be seen
from a distance. See how the colors form a transition from yellow
to dark brown. There is an obvious intent to create not only different
colors but also to create a transition between the colors. Note
the interspersed blueish scales that create a sheen on the wing
without changing the lovely underlying dark brown color.

A Creator designed this butterfly and He intended the colors on
its wings to be complimentary brown and yellow and gold and to exhibt
accents of yellow that fade into the dark brown background. And
He created a bluish sheen that would shimmer in the sunlight.

This pattern and the colors are expressed not only on the wing,
but are also written into a language (or code) that is expressed
by the arrangement of the atoms of the DNA of this insect. It is
this code (this arrangement of atoms and the molecules that the
atoms compose) that describes and determines the chemical composition
and the size and the color of each of thousands of individual scales.

Somewhere in the molecular structure of this insect there are atoms
arranged into a code that defines precisely where each of these
scales will be placed in order to form the design. The code specifies
the row and the number and where the brown and the yellow and the
transition between the yellow and the brown will be placed. This
design was intended before the scales were colored, and the code
had to be conceived before the atoms and molecules could be arranged
in the correct sequence to utilize it.
In order to argue that this insect was not the product of a Creator,
evolution must make a presumption. And that presumption is simply
that one cannot consider whether or not a Creator created because
that consideration is outside of the realm of accepted science.
Such a consideration is not science. Since it is not science, it
cannot be considered as an answer to a scientific question.

Therefore, accidental mutations and survival of the fittest wrote
the design of the butterfly's wings into a code inscribed in a sub-molecular
structure inside the cells that make up the insect. The same unobserved
process provided the mechanism for the interpretation of that code
and then utilized that interpretation to assemble the wings, placed
each scale on each row in its place and simultaneously constructed
the brain of the insect that operates the wings and computes at
the rate of a trillion organized cycles per second.

Since evolution is founded upon the presumption that there is no
God, any actual evidence for special creation is quite irrelevant
to evolutionists:

Evolutionists don't really care if there is evidence for creationism
because their system of belief renders God to be a nullity no matter
what the evidence shows. So, to evolutionists, creationism is untenable
ab initio no matter what. Evolutionists refer to this as "rational
thought." Ironically, this rational thought is nothing more
than a theological conclusion. See antiscientific argument.

Environmental pressures have just as much chance of transforming
caterpillar into a butterfly as transforming an evolutionist into
a Christian - or as much chance of creating a supercomputer the
size of a pinhead. God exists and only God can do these things.